920.1 General
Unit heaters must be installed in accordance with their listing and manufacturer instructions. Oil-fired unit heaters must be tested in accordance with UL 731.
920.2 Support
Suspended-type unit heaters require support elements designed and constructed to accommodate the unit heater weight and dynamic loads. Hangers and brackets must be noncombustible.
Suspended-type oil-fired unit heaters must also be installed in accordance with NFPA 31. Section 920.2 references that standard; it does not reproduce its installation criteria.
920.3 Ductwork
A unit heater cannot be attached to a warm-air duct system unless listed for that installation. This is a listing-dependent restriction, not a blanket prohibition on duct attachment.
920.4 Prohibited uses
In Group I-2 and ambulatory care facilities, suspended-type unit heaters are prohibited in:
Corridors
Exit access stairways and ramps
Exit stairways and ramps
Patient sleeping areas
Keep the scope precise: the prohibition addresses suspended-type units in these specified spaces.
Why it matters
Equipment approval, support design and location suitability are separate checks. A listing does not override a prohibited location. Noncombustible hangers alone do not establish adequate support for weight and dynamic loads.
Where to show it
Mechanical schedule: unit type, model and installation requirements
Architectural plans: occupancy and room use
Support details: attachment and design loads
Submittals: listing, manufacturer instructions and duct-connection eligibility
Do
Check occupancy and room use before selecting the location.
Coordinate support with the selected unit.
Verify NFPA 31 requirements for suspended oil-fired units.
Do not
Approve a duct connection based only on physical fit.
Treat existing hangers as proof of adequate support.
Field tip
For a replacement, verify what the hangers actually connect to. Trace the load path to the supporting structure and review it for the new unit's weight and dynamic loads. Next: #192, IMC 921 Vented Room Heaters.
In Florida
In Florida the mechanical code is the 2023 FBC-Mechanical (8th Edition), which is based on the 2021 IMC and generally follows the same Chapter 9 numbering. Confirm the Florida section text, any Florida amendment and the referenced standard editions before relying on a 2024 IMC detail. The 9th Edition applies to permit applications on or after 12/31/2026 (state adoption pending).
Questions to settle before design
What is the room use and occupancy? Group I-2 and ambulatory care have prohibited locations.
What structure will carry the hangers, and who designs the support for weight and dynamic loads?
Will the unit attach to a warm-air duct system? If so, is it listed for that?
MasterBuild field checklist
Trace each hanger to the supporting structure.
Confirm hangers and brackets are noncombustible.
On a replacement, compare the new unit's weight with the existing support's capacity.
MasterBuild recommendation: process steps for design and site review, not code text.
Where MasterBuild helps
PE-led MEP design in Miami, or send your project background. The fee is quoted in writing before work starts.
Code basis
2024 IMC Section 920 model-code education from the owner-published Daily Code Talk. Confirm the locally adopted edition and amendments, the selected product listing and manufacturer instructions, and the authority having jurisdiction. Read the ICC 2024 IMC Chapter 9 for the complete model-code provisions.